A project is proposed to develop an ultrasensitive enzyme immunoassay for specific viruses that is expected to be more sensitive than any currently existing technology for that purpose. This proposed assay involves virus-triggered release of microencapsulated enzyme. The assay is noncompetitive, (i.e. it does not involve competition between virus to be detected and labeled viral antigen), involves effective activation of a large number of enzyme molecules for each virus incorporated into the assay system, and is expected to have a very low background. The primary value of this technology is expected to be for prevention of viral diseases by being able to detect very low levels of pathogenic viruses in, for example, human blood and blood components used for therapeutic applications, and certain foods and water used for human consumption. The goal of a Phase I project is to develop methods for preparation of components of the assay having the required characteristics. The Phase I development work should then allow preparation and optimization of laboratory prototypes of such assays in a Phase II project.